--- Chimichurri ---
Combine the vinegar, lime juice, garlic, and shallot in a food processor and mix on low speed.
Drizzle in the olive oil while mixing; the dressing will begin to emulsify.
Add the cilantro, parsley, salt, and pepper and continue to mix on low until the dressing is uniform in texture and the herb pieces are chopped quite small.
Chimichurri will last 2 to 3 days in the refrigerator. If making ahead, bring it to room temperature before serving. If the dressing has separated, gently whisk to reblend.
--- Kabobs ---
If using wooden skewers, soak them in water for 30 minutes to 1 hour to prevent them from burning.
Place the steak in a resealable plastic bag or nonreactive bowl with a lid. Cover the steak with enough chimichurri (about 1 cup) to coat thoroughly. Seal the bag or cover the bowl and marinate the steak in the refrigerator for 1 to 8 hours; more is better, especially for tougher cuts. (Feel free to leave your steak marinating overnight, or start your dinner prep in the morning before work.)
Remove the steak from the refrigerator 30 minutes before cooking. Preheat the grill to high heat (500°F).
Remove the steak from the marinade; discard the marinade. Prepare the kabobs by threading the steak, bell pepper, onion, and zucchini onto soaked wooden skewers or metal skewers, alternating meat and vegetables. You should be able to make about 6 skewers.
Grill the kabobs directly over high heat for 2 minutes on each side. Reduce the heat to medium (or move the kabobs to indirect heat) and brush with the remaining 1/2 cup chimichurri. Grill to desired doneness, 12 to 15 minutes. (The easiest way to check is to remove one of the kebabs from the heat and cut into the meat, checking for color.)
If you don’t have a grill, you have two other options for the kabobs. First, buy a grill plate for your stove and follow the same directions—it’s just like a barbecue, minus the mosquitoes. Or, you can broil, and then bake the skewers: Preheat the oven to Broil (or 500°F) and place the skewers on a foil-lined baking sheet. Broil the kabobs for 3 minutes, then flip the skewers and broil for another 3 minutes. Reduce the oven temperature to 350°F and brush the skewers with the remaining chimichurri. Bake to desired doneness, 12 to 15 minutes.